Patients with these tumors, which are characterized by single-file morphology and loss of E-cadherin expression, have been convincingly shown to experience patterns of survival indistinguishable from patients with the more common invasive ductal carcinoma [35], yet the diagnosis of lobular carcinoma is routine, critical for appropriate long-term clinical management and highlights a patient subgroup potentially amenable to novel targeted therapies. The gene discussed is CDH1; the disease is invasive ductal breast carcinoma.